Pulse group discriminator



Aug. 21, 1951 C. H. HOEPPNER PULSE GROUP DISCRIMINATOR Filed Nov. 14,1945 '7 Sheets-Sheet 1 HIGH 3 PULSE FREQUENCY GROUP REcEIvER STAGEDISCRIMINATOR PULSE RECEIVING SYSTEM 3 PULSE TIME WIDTH INTERVALDISCRIMINATOR GENERATOR TIME INTERVAL GENERATOR i 7 lo PIE,

TIME

INTERVAL GENERATOR 115;.5

TIME INTERVAL GENERATOR gIwIz/wtom CONRAD H. HOEPPNER 1951 c. H.HOEPPNER 2,54,92

PULSE GROUP DISCRIMINATOR Filed Nov. 14, 1945 7 Sheets-Sheet 5 2-2 WE-1%; T 80 swam T490 CONRAD H. HOEPPNER 8" 1951 c. H. HOEPPNER 2,564,92

PULSE GROUP DISCRIMINATOR Filed Nov. 14, 1945 7 Sheets-Sheet 4 ILELE I II Law I l I I I I r w L; W L

93 I I I I I I I I I 94 I I I I I I I 95 F L i m 96 I I I I 97 FL T11;

Lil y- 95x SHAW/14m CONRAD H. HOEPPNER Aug. 21, 1951 c. H. HOEPPNER 9 5PULSE GROUP DISCRIMINATOR Filed Nov. 14, 1945 7 Sheets-Sheet 5gjwue/wbo't CONRAD H. HOEPPNER Aug. 21, 1951 c. H. HOEPPNER 2,554,692

PULSE GROUP DISCRIMINATOR Filed Nov. 14, 1945 7 Sheets-Sheet 6 I I I I Il I I I I MM '33 l I I I v I I I I I I34 l I I36 I I I I37 I L .38

Swim I304; OWRAD H. HOEPPNER Aug. 21, 1951 c. H. HOEPPNER 2,564,692

PULSE GROUP DISCRIMINATOR Filed Nov. 14, 1945 7 SheetsSheet 7 I IE; E

* PULSE TIME WIDTH INTERVAL DISCRIMINATOR GENERATOR 1 PULSE TIME WIDTHINTERVAL DISCRIMINATOR GENERATOR PULSE TIME WIDTH INTERVAL DISCRIMINATORGENERATOR PULSE TIME 55 WIDTH INTERVAL J oIscRIMINAToR GENERATOR coNRAoH. HOEPPNER Patented Au. 21, 1951 UNITED ST amended April 30, 1928; 370O. G. 757) This invention relates in general to electronic circuitshaving discriminatory response characteristics and in particular to anelectronic circuit for pulse group structure discrimination.

2 mined duration predeterminedly spaced in time. It is another object ofthis invention to provide a circuit which is responsive only to aparticular pulse group structure and which may not be ren- In radio,radio detection, television, and other 5 dered unresponsive thereto bythe prior applicaelectrom'c fields, it frequently occurs that a numtionof electrical impulses not arranged in that her of different potentialvariations may exist at particular pulse group structure. the input toa. component electronic circuit either It is another object of thisinvention to profortuitously or by intention. If all of such variavide acircuit which may be employed between a tions are not to be impressedupon the composource of potential variations or electrical imnentcircuit, it is e ssary to provide an intervenpulses and the receiverthereof as an intervening ing circuit with the ability to discriminatebecircuit which shields from such receiver all variatween thosevariations intended for ultimate aptions or pulse groups except thosehaving a cerplication to the component circuit and those varitaindefinite group structure. ations the eifect of which would beundesirable. It is another object of this invention to pro- Somecharacteristic or characteristics of the povide a method of shieldingfrom a signal retential variations must be selected as a basis forceiver all electrical impulses not of a predeterpulse discrimination andamong such charactermined duration predeterminedly time related. isticsare time duration, pulse spacing, polarity, It is another object of thisinvention to prorate of change, and amplitude. vide a method ofproducing an output signal in Given such a basis and a suitableintervening response only to electrical impulses of a p circuit, manyuseful applications may result. For termined duration predeterminedlytime related example, a means of pulse coding is provided in in such amanner that preceding electrical imwhich intelligence is conveyed bymeans of elecpulses do not interfere with the production of tricalimpulses endowed with the chosen characthat output signal. teristic inthe form in which it will be favored by Other objects and features ofthis invention will the receiver of the message. All those electricalbecome apparent upon a careful consideration of impulses not so endowed,whether they be delibthe following detailed description when takentoerately introduced so as to disguise a communigether with theaccompanying drawings in which: cation for secrecy purposes or reach thereceiver Fig. 1 is a simple block diagram of a pulse refrom man-made ornatural sources so as to conceiving system utilizing one embodiment ofthis stitute accidental or deliberate interference, are invention;rejected by the intervening circuit. An obvious Fig. 2 is a simple blockdiagram of one embodiextension of such a pulse coding system is toproment of this invention; vide a receiver with a plurality ofintervening Fig. 3 is a circuit diagram of one of the forms circuits,each so constructed as to select and favor which the embodiment of Fig.2 may take; its particular type of electrical impulses. In this Figs. 4,5, 6 and '7 represent series of waveway a multiplicity of communicationchannels forms useful in explaining the operation of the may beprovided. The endowment of electrical circuit of Fig.3; and impulseswith the chosen characteristic in the 4) Fig. 8 is a simple blockdiagram of a variant form in which they will be favored does notnecembodiment of this invention. fl y perate to prevent a variation inanother In order to accomplish certain of the objects characteristicwhich can be put to a useful purof this invention, a means of rejectingapplied pose. Thus, pulses which may be restricted as to electricalimpulses not having predetermined time duration and spacing so as to befavored by duration characteristics is employed for the dual a pulsegroup discrimination circuit, may also be amplitude modulated so as toconvey intelligence or provide a second means of discrimination.

It is an object of this invention to provide a circuit which isresponsive only to pulse groups comprising pulses of a predeterminedduration predeterminedly spaced in time.

It is another object of this invention to provide 'a circuit which isresponsive only to a predetermined number of electrical impulses ofpredeterpurpose of repulsing the majority of video signals which mayarise from any unrestrained source and of limiting the total number ofsignals which may be effectively received in a given interval. of time.In combination with this means, which may be termed pulse widthdiscriminator means, is employed a sequence of time interval generatorseach responsive to the output of the pulse width discriminator means.Each member of the sequence of time interval generators except the firstis held unresponsive except during the time interval generated by themember immediately preceding it in the sequence. By properpredetermination of the duration of the time intervals generated by themembers of the sequence, this combination provides that the last memberof the sequence remains unresponsive and fails to generate its timeinterval unless each precedent member is caused to generate, in turn,its respective time interval and further that a sufficient number ofelectrical impulses of certain characteristics of duration must beapplied to the pulse width discriminator in a given interval to causethe last member of the sequence to generate its time interval. Adistinguishing feature of this invention is that, by virtue of theability to make a proper predetermination of the respective timeintervals, the pulse group discriminator remains oblivious to electricalimpulses which might otherwise render it unresponsive to a desired pulsegroup. This feature, which arises from the limited memory characteristicof the circuit will be more fully explained in the paragraphs whichfollow.

For preliminary explanation, reference is now had to Fig. 1 which isillustrative of a pulse receivingv system wherein a pulse groupdiscriminator is employed to repulse undesired video signals. Pulses orbursts of high frequency energy received by antenna I, amplified anddetected by high frequency stage 2 are impressed, in the form of theenvelope of the high frequency pulses of energy, to input 3 of pulsegroup discriminator 4. Since the groups of pulses of high frequencyenergy reaching antenna I may comprise not only a desired signal butalso manmade and fortuitous interfering signals of a frequency whichhigh frequency stage 2 will not reject, it is the function of pulsegroup discriminator 4 to shield from receiver 5 all pulse groups nothaving the group structure characteristics of the desired signal.

In Fig. 2, pulse group discriminator 4 is shown in block diagram form.Pulse width discriminator 6 represents apparatus which applies atriggering pulse to parallel feeder lead I only if an electrical impulseexceeding in duration a predetermined duration is applied at input 3.Blocks 8, 9, l0, and II represent a sequence of generators each of whichmay generate pulses defining time intervals of any desired duration.Connecting the sequence of time intervals generators are connections [2,l3, and M, which represent the medium by which any given member of thesequence holds the immediately subsequent member of the sequenceunresponsive to trigger pulses except during the time interval definedby the pulse generated by that given member.

In operation, pulse width discriminator 6 receives electrical impulsesat input 3 and produces a triggering pulse at I only in response to eachof those electrical impulses which exceed in duration a predeterminedduration. Were the time interval defining pulses generated by generators8, 9, and i0 of infinite duration, any four electrical impulses receivedby discriminator 6 having the predetermined duration characteristics,regardless of the length (greater than the minimum length) andregardless of the spacing between pulses, would eventually causegenerator H to produce its pulse. The first triggering pulse at lead Iwould cause generator 8 to function and thereby ready generator 9 torespond to the next trigger pulse. The second triggering pulse(separated from the first by at least the pulse width requirement ofdiscriminator 6) would cause generator 9 to respond and thereby readygenerator H] for the third trigger pulse. This process would continueuntil the fourth trigger pulse caused generator II to function. If,however, the time intervals defined by the pulses produced by generators8, 9 and I 0 are limited, the four electrical impulses which can passdiscriminator 6 must all arrive within a predetermined interval of time.That predetermined interval of time is definedby the sums of the maximumspacings which may occur between triggering pulses without the pulsegenerated by any member of the sequence terminating before thesucceeding member of the sequence is caused to generate its timeinterval. An output signal, may, of course,- be taken from the lastmember of the sequence or from any combination of members of thesequence. In the first case, the output signal will be produced onlywhen four triggering pulses are produced within a predetermined intervalof time by discriminator 6. In the second case, an output signal will beproduced only when all of the selected combination of members aresimultaneously generating their time interval. defining pulses. It willbe seen that, for generator I I to be caused to function, the timeinterval generated by 9 must lap that generated by 8, the time intervalgenerated by Ill must lap that generated by 9, and that the intervalgenerated by II will lap that generated by III. This requirement pointsup the fact that the triggering pulses must be time related in apredetermined manner and that the character of this manner may becontrolled by predetermination of the time intervals generated by themembers of the sequence.

In Fig. 3 is shown a preferred form of circuit for the embodiment ofthis invention. Vacuum tubes It, It, l7 and I8 together with theirassociated circuit elements comprise a means of producing triggeringpulses at lead I9 from each of only those electrical impulses applied atinput 3 which possess certain predetermined duration characteristics.There are other circuit arrange-- ments which may be employed to achievethe same purpose but this one has been selected since its operation isdescribed in detail in my copending application, Serial No. 608,804,entitled Pulse Width Discriminator filed August 3, 1945, now Patent No.2,534,264, dated December 19, 1950. Briefly, a negative electricalimpulse applied at input 3 drives tube l5 below cutoff and causescapacitor 20 to charge up in a nearly linear manner for the duration ofthe applied impulse and then to discharge rapidly as tube I5 is againrendered conducting at the end of the impulse. This will be recognizedas a conventional sawtooth generator the output of which is applied bothto grid 2| of tube l6 and grid 22 of tube IT. The amplitude of theoutput sawtooth which is applied to tubes l6 and H is, of course, afunction of the duration of the applied electrical impulse.

Tube It is so biased at its cathode by the voltage divider between B+potential and ground comprising resistors 23 and 24 that the sawtoothmust achieve an amplitude corresponding to a predetermined minimumduration of electrical impulse at input 3 before grid 2| is raised highenough in potential to allow tube It to conduct. When that minimumduration occurs and that cqllesponding amplitude is achieved, arectangular negative pulse appears at plate of tube l6 of a durationdetermined by the interval of time between the unbiasing of tube IS andthe end of the electrical impulse applied at input 3. This rectangularnegative pulse is differentiated by the circuit comprising capacitor 25and resistor 2'! so as to apply a sharp positive pulse to grid of tube18 at the end of the rectangular negative pulse (and hence at the end ofthe ing to an applied electrical impulse of greater duration is requiredbefore tube I! will conduct. When tube l1 conducts, its plate goesnegative and biases ofl tube l8 at grid 3!. Resistor 32, through whichcapacitor 33 recovers its charge after tube I? is rendered conductingand then non-conducting, is of such a value that plate 3 of tube I!rises slowly at the end of an applied electrical impulse at input 3 of aduration great enough to unbias tube l1. Thus, if an impulse of aduration less than that required to unbias tube H5 is applied to input3, no triggering pulse is produced by tube 18 and applied to lead it. Ifan impulse of a duration great enough to unbias tube l5 but too small tounbias tube I! is applied to input 3, a triggering pulse is produced bytube I 8 and applied to lead l9. If, however, tube It is unbiased, itholds tube l8 cut off during the short interval when tube it wouldordinarily render it conducting to produce a triggering pulse. By thismeans, both underwidth and overwidth discrimination is accomplished.Tube 315 represents a phase inverter of common arrangement so disposedthat the nega tive triggering pulses appearing on lead l9 becomepositive triggering pulses when they appear on lead 3? at the output ofthe phase inverter.

Dual triode tubes DlL and DIR represent the vacuum tube components of aconventional "onekick or delay multivibrator which has only one stablestate of equilibrium (DlL conducting and D! R. non-conducting) but whichwill maintain, upon receipt of a negative triggering pulse at grid 38 ofDlL, a second state (DiR- conducting and DI L non-conducting) for adefinite interval of time. The time interval for which the second stateof the multivibrator can be maintained is determined substantialh, bythe time constant circuit formed by condenser 3Q, resistor 49, andresistor ii in the plate circuit of tube !8. As tubes DEL and DiR aredriven into non-conduction and conduction respectively to produce thepositive pulse at plate circuit Q2 of tube DIL which defines the timeinterval, plate circuit 43 of tube DlR is driven sharply negative andcondenser 39, which is fully charged, holds grid 38 of tube DIL belowcutofi until it partially discharges through resistors 4c and M. Withinfairly wide limits the duration of the time interval defined by thepositive pulse which appears at plate circuit :12 may be varied byvariation in the value or" resistor 25}. It will be seen that dualtriode tubes DZL-D2R, D3L- D33, and DfiLD iR are similar onekiclmultivibrators each of which may be employed to generate a time intervaldefining pulse of in dependently selectable duration.

One of the principles upon which this invention is based is that such aself-returning or one-kick multivibrator has only one stable operatingstate but once triggered, obligingly assumes a second or unstable statefor a definite interval of time. At the end of that interval, it insistsupon returning to the quiescent stable state originally existing. Thusthe multivibrator may be said to have a limited memory in that itremembers only for a definite interval having been triggered. at the endof which it promptly forgets the triggering action and is prepared foranother limited memory cycle. On the other hand, an electronic switchtype or" counter, while it is also a member of the multivibrator family,has, in its simplest form, two stable states either of which it willmaintain indefinitely if undisturbed. Thus, the electron switch counter,having once been triggered, is unable to forget that action of its ownfree will. This inability to forget is also characteristic of otherelectronic counters, such as the condenser type counter, inasmuch astheir counting function requires that they remain substantially passivebetween the applied units being registered.

Another of the principles upon which this invention is based is that ifa plurality of selfreturning multivibrators be so connected in sequencethat each multivibrator, except the first, is unresponsive to triggeringpulses except during the second (unstable) state of the immediatelypreceding multivibrator, the limited memory characteristics of theindividual multivibrators may be employed to define an interval of timeduring which at least one triggering pulse corresponding to eachmultivibrator must be applied to the sequence in order to cause all themultivibrators to be simultaneously in their second states or to causethe last multivibrator to assume its second state.

Still another principle upon which this invention is based is that if aplurality of self-returning multivibrators be connected as describedabove, the limited memory characteristic of each of the individualmultivibrators may be employed to render inefiective triggering pulsesapplied to the sequence of multivibrators which do not occur in aspecified time relation.

In Fig. 3, tubes Si, S2, and S3 represent a plurality of shielding meanselectrically disposed between successive members of the sequence ofmultivibrators DlL-DIR, D2L-D2R, D3LD3R, and DLD4R and between the pulsewidth discriminator means and a respective member of that sequenceexcluding DILDIR. These shielding tubes operate to hold eachmultivibrator, except the first, unresponsive to triggering pulsesexcept during the existence of the time interval defining pulsegenerated by the immediately preceding multivibrator. For example, itwill be seen that shielding tube SI receives its grid Msignals fromDill-DIR and communicates its plate 55 signals to D2LD2R and thusconnects precedent member DILDIR of the sequence to subsequent memberDZL-DZR. It will also be seen that triggering pulses produced by thepulse width discriminator at lead 37 of inverter tube 36 are connectedthrough shield tube SI (via grid 46) to associated subsequent memberD2L-D2R of the sequence (via plate circuit 45). Similarly, shieldingtubes S2 and S3 connect succeeding members of the multivibrator sequenceto each other and to the pulse width discriminator. Grid 44 of tube SIis returned through resistors 41 and 48 to plate circuit 42 of DIL andthrough resistors 41 and 49 to C- potential and resistors 41, 48, and 49have been chosen of such a value that tube SI may only conduct when DILis non-conducting to produce the positive time interval defining pulseat plate circuit 42. Grid 45 of tube SI is returned through resistors 50and I to C potential and through resistors 59 and 52 to ground in such amanner that tube SI may only conduct when the pulse width discriminatorcauses a positive triggering pulse to appear on lead 31 and to beappliedto grid 46 through capacitor 53. When the two conditions for theconduction of SI are established, i. e., DIL-DIR generating its timeinterval defining pulse and the pulse width discriminator producing atriggering pulse, a negative triggering pulse appears at plate circuit45 of tube SI to trigger the associated subsequent member of thesequence, D2L-D2R. Tubes S2 and S3 perform similar functions for theirassociated precedent and subsequent members of the sequence ofmultivibrators. If four triggering pulses are produced in the propertime relation by the pulse width discriminator, the members of thesequence generate their time interval defining pulses in succession anda negative pulse of a duration equal to the time interval generated byD4L-D4R is produced by plate circuit 54 of DAR. and appears at outputterminals 55. This negative pulse at terminals 55 may be communicated toreceiver 5 of Fig. 1 and constitute the output signal which indicatesthe receipt of a pulse group of proper structure at input 3. Likewise anamplitude responsive means such as tube 55 ma be connected to selectedmembers of the sequence of multivibrator in such a manner that itresponds only when those selected members simultaneously generate theirinterval defining pulses. In Fig. 3, tube 55 has its grid 5'! connectedto all members of the sequence through lead 58 and is so chosen that itconducts only when DIL, D2L, D3L and D413 are all non-conducting. Thiscondition occurs only when all members of the sequence are generatingtheir time intervals simultaneously and causes a negative output signalto appear at terminals 59.

In Fig. 4 are shown several Waveforms representative of the voltagevariations (with respect to time on the horizontal axis) which occur inthe circuit of Fig. 3 when electrical impulses are applied at inputterminals 3. These waveforms may be produced under conditions in whichthe time intervals generated by the members of the sequence areprogressively shorter. The interval of DILDIR has been adjusted byproper choice of resistance 49 to be just slightly longer than threetimes the minimum width of an electrical impulse which will cause thepulse width discriminator to produce a triggering pulse. Thus threetriggering pulses may be produced if properly time related to thetriggering pulse which triggers DIL--DIR during the interval which DILDIR generates. Similarly, the interval of D2LD2R has been adjusted byproper choice of resistor 62 to be just slightly longer than two timesthe minimum electrical impulse width and the interval of D3L-D3R hasbeen adjusted to be slightly longer than that minimum electrical impulsewidth. The interval of D4L-D4R has been adjusted to provide an outputsignal of convenient duration at terminals 55 and 59. Of the waveformsin Fig. 4;, waveform 19 represents a series of four negative electricalimpulses 19A,

8 19B, 10C and 10D, each of which just equals the minimum durationrequired to cause a triggering pulse to appear on lead I9. The fourresulting negative triggering pulses, each of which corresponds in timeto the trailing edge of a respective pulse group, are represented bywaveform II. Negative pulse HA is communicated to the first member ofthe sequence of multivibrators DILDIR via lead 69 and causes it tofunction to generate time interval defining pulse 12A of waveform I2 atplate circuit 42. The remaining pulses NB, "NC, and MD of waveform IIare impotent insofar as DIL-DIR is concerned since DI L is held belowcutofl during the interval which the multivibrator generates. The pulsesof waveform II are also inverted by tube 36 to appear on lead 3'! as theseries of four positive triggering pulses shown by waveform I3. Pulse13A raises the second control grids of all the series S shielding tubesabove cutoff potential, typified by the raising of grid 46 of tube SIabove cutoff but conduction is prevented by the fact that no member ofthe sequence is generating its time interval. Pulse 13B again raised theS series second control grids above cutoff and is able to cause SI toconduct since the first member of the sequence was caused to function bytriggering pulse HA. The culmination of this process is demonstrated bywaveform M which represents the triggering pulses applied to D2LD2R,waveform 15 represents the time interval defining pulse generated byD2L-D2R, waveform 16 represents the triggering pulses applied to D3LD3R,waveform 11 the pulse generated by D3LD3R, waveform 18 the triggeringpulse applied to D4LD4R, waveform '19 the pulse generated by D4LD4R,waveform 89 the voltage variations appearing at grid 51 of tube 55, andwaveform 8| the output signal at terminals 59. If the output be taken atterminals 55, waveform 89 also represents the expected output signal. Itwill be seen that had any of the electrical impulses comprising thegroup applied at input 3 been of too small or too great a duration orhad the spacing between any of the pulses been extended, the timerelation of the triggering pulses produced would have been such as toallow one or more of the time intervals generated to terminate before atriggering pulse could get through to cause the next time interval to begenerated. Thus, an output signal is produced only in response to apredetermined number of triggering pulses produced within apredetermined interval of time. Likewise it will be seen that an outputsignal is produced only when the time interval generated by D2LD2R lapsthat generated by DIL--D.IR, the time interval generated by D3L-D3R lapsthat generated by D2L-D2R, and the time interval generated by D4L-D4Rlaps that generated by D3L--D3R. In the case of the output signal atterminals 59, it will also be seen that this is produced only when thetime intervals generated are coexistent so as to produce waveform 89. Asfor the output signal at terminals 55, this may be expected wheneverDAL-DAR is caused to function. Illustrative of the foregoing are thewaveforms of Fig. 5 in which waveform 99 represents a series ofelectrical impulses applied to input 3. Waveforms 9| through I9Icorrespond in significance to Waveforms II through 8| of Fig. 4. Inwaveform 99, impulses 99A, B, 90C, and 90D would produce an output atterminals 55 and 59 except for the fact that the spacing between 99C and90D is so great that the time interval generated by D3LD3R, asillustrated by waveform 91, is ended before trigger- 9 ing pulse SID ofwaveform 9| can cause D4LDAR to function. Thus, the bias on tube 56never is removed suificiently to allow the grid potential to rise abovelevel 0. 0. tube 58 indicated on waveform I69 so as to produce an outputpulse at 59. Likewise, D4L--D4R is never caused to function so that nooutput signal appears at terminals 55. Reverting to waveform 90, it willbe seen that impulse 90E is too wide to produce a trigger pulse and thatimpulse 98F, is too narrow. The remaining pulses are all of the properduration characteristics, however, and pulses IBIJ and IGIL appear atthe outputs. In certain respects the performance is satisfactory sincepulses 90A, 90B, 98C, 99D, 90E, 99F, BBQ, and 90H all failed to producean output pulse at either 55 or 59. The mere fact that two output pulsesIIHJ and IUIL were produced when the proper impulse group comprising991, SM, 90K and ML was impressed at input 3 is of slight importancesince receiver 5 of Fig. 1 may be so constructed to register only thefirst of two pulses received so closely spaced. The fact, however, thatimpulses 99K and 95L could have been missing and there still have beenproduced at 55 and 59 output pulse If! IJ is important since this would"constitute a condition in which a series of electrical impulses producedan output signal even though no pulse group of the specified structurewas present. This trouble may be remedied with respect to output 58 byconstructing all but the last multivibrator in the series in such amanner that the rise time of the positive interval defining pulse isslow. For example, had the rise time of pulse 95J of waveform 95 beenslow enough, pulse 99J of waveform 99 would have disappeared beforewaveform I05 reached level C. 0. tube 56 as at IBISJ. In thisconnection, the distributed capacitance to ground associated with thefirst control grid circuits, typified by grid 44 of tube SI, of theshielding tubes has been found sufiicient to prevent a. singletriggering pulse from causing two successive members of themultivibrator sequence to function.

A somewhat diiferent predetermination of the time intervals of thesequence members increases the specificity of the circuit of Fig. 3.This merely involves so choosing resistors 45, B2, and 6| associatedwith the first three members of the sequence that the interval generatedby each is justly slightly more than the minimum pulse width whichproduces a triggering pulse. Fig. 6 illustrates the response of thecircuit so operated to an impulse group identical to that shown bywaveform I6 of Fig. 4. As shown by this figure, in which waveforms IIUthrough I I9 have the same significance as waveforms I0 through 19 ofFig. 4, and waveform I2I corresponds to waveform 8|, an output pulse issecured at output 55 only when a negative pulse is produced in platecircuit 56 of DAR.

Fig. '7 emphasizes the advantage of this type of operation and shows theresponse of the circuit to a series of electrical impulses similar tothat shown by waveform 9B of Fig. 5. In Fig. '7, waveforms I30 throughIM have the same significance as waveforms IID through I2I of Fig. 6. Byvirtue of the fact that no output signal appeared at terminals 55 untilthe four impulse group comprising I301, l3liJ, I30 K and I30 L ofwaveform I36 was applied to input 3 as shown by waveform MI isdemonstrated by the fact that the pulse group discriminator possessesboth high specificity and great reliability. It not only refused torespond to pulse groups not having 10 the predetermined structure but italso remained oblivious to those non-regulation groups when the timecame to examine the proper group structure. This last feature is onewhich distinguishes it from a pulse group discriminator not having thelimited memory feature. For example, one might construct a discriminatoremploying a scale-of-four electronic counter automatically reset by atime interval generator. Such a discriminator would operate well toreject nonregulation groups but it is easily duped by one or moreimpulses preceding a proper impulse group into a condition in which itwill fail to respond to that group for which it was intended. Thecircuit of Fig. 3, when operated as last described, ignores impulses notpart of a proper impulse group.

To those versed in the art will occur a number of interesting changesin. circuitry and operation. For example, the specificity of the circuitmay be increased further by providing a plurality of pulse widthdiscriminators rather than one and so connecting them to themultivibrator sequence that each member of the sequence is caused tofunction in response to an electrical impulse of a different width.There are obviously a considerable number of permutations available andsuch a construction heightens the secrecy element in a communicationsystem of which a receiving system is shown in Fig. 1. In Fig. 8 isshown in block diagram this variational arrangement. Pulse widthdiscriminators I50, I5I, I52, and I53 each have a particular impulseduration to which they respond and if the correct duration impulses inthe proper order, all within a predetermined interval of time are notapplied to input 3, no output signal appears at terminal 55.

Reverting now to the circuit of Fig. 3, it will be seen that the pulsewidth discriminator shown having both underwidth and overwidthcharacteristics may be replaced by a pulse Width discriminator havingonly the characteristic of underwidth discrimination. Any pulse of toogreat a duration, even though it produced a trigger pulse would find orcreate a condition in which one of the time intervals would end before asubsequent triggering pulse could be produced.

Other changes include other output connections such as selecting onlycertain of the members of the sequence for unbiasing an output tube. Amere change in the number of members of the sequence may be made withoutexceeding the limits of this invention and results only in decreasing orincreasing the specificity of the circuit.

It will be apparent that a pulse group discrimination circuitconstructed in accordance with the teachings of the invention will havea wide variety of applications in radio, radio detection, television andother electronic fields whenever discrimination between voltagevariations is desirable and the time durations of individual variationsin a group of pulses and the time relations of these variations can beused as the basis for such discrimination. It will also be apparent thata pulse group discrimination circuit constructed as taught by thisinvention may be used in combination with other circuits, alsodiscriminatory in response, whose action is based on othercharacteristics of the input signal such as amplitude; polarity, or rateof change.

Since certain further changes may be made in the foregoing constructionsand different embodiments of the inventions may be made withoutdeparting from the scope thereof, it is intended that all matter shownin the accompanying drawings or set forth in the accompanyingspecification shall be interpreted as illustrative and not in a limitingsense.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. A pulse group discriminator comprising, means for producingtriggering pulses in response to applied electrical impulses havingpredetermined duration characteristics, a sequence of pulse generatingmeans for generatin impulses of differing fixed durations in response tosaid triggering pulses, each member, except the first, of said sequencebeing so constructed as to be unresponsive to said triggering pulsesexcept during the existence of an impulse generated by the member ofsaid sequence immediately preceding, and means for producing an outputsignal only when the last member of said sequence generates its impulse.

2. A pulse group discriminator comprising, means for producingtriggering pulses in response to applied electrical impulses havingpredetermined duration characteristics, a sequence of pulse generatingmeans for generating impulses of differing fixed durations in responseto said triggering pulses, a plurality of shieldin means for theselectable application of said triggering pulses to the members of saidsequence, said shielding means each disposed between first said meansand a respective member, except the first, of said sequence and betweentwo successive members of said sequence, and means for producing anoutput signal only when the last member of said sequence generates itsimpulse.

3. A pulse group discriminator comprising, pulse width discriminatormeans producing triggering pulses from applied electrical impulses, asequence of multivibrator means each for generating a time intervaldefining pulse in response to a triggering pulse, a plurality ofshielding tubes each connecting two successive members of said,sequence, said pulse width discriminator means being connected to thefirst member of said sequence and, through each of said plurality ofshielding tubes, to each of the succeeding members of said sequence, andmeans producing an output signal only when the last member of saidsequence generates its time interval defining pulse.

4. A pulse group discriminator comprising, pulse width discriminatormeans produciing triggering pulses from applied electrical impulses, asequence of multivibrator means each for generating a time intervaldefining pulse in response to a triggering pulse, a plurality ofshielding tubes each connecting a precedent member and a subsequentmember of said sequence, each of said shielding tubes being soresponsive to the pulse generated by its associated precedent memberthat, only during the time interval defined thereby does said shieldingtube permit the application of triggering pulses to its associatedsubsequent member, said pulse width discriminator means being connectedto the first member of said sequence and, through each of said pluralityof shielding tubes, to each of the succeeding members of said sequence,and means producing an output signal only when the last mem- 12 ber ofsaid sequence generates its time interval defining pulse.

5. A pulse group discriminator comprising, pulse width discriminatormeans producing trig= gering pulses from applied electrical impulses, asequence of multivibrator means each for generating a time intervaldefining pulse in response to a triggering pulse, a plurality ofshielding tubes each connecting a precedent member and a subsequentmember of said sequence, each of said shielding tubes being soresponsive to the pulse generated by its associated precedent memberthat, only during the time interval defined thereby does said shieldingtube permit the application of triggering pulses to its associatedsubsequent member, said pulse width discriminator means being connectedto the first member of said sequence and, through each of said pluralityof shielding tubes, to each of the succeeding members of said sequence,and means producing an output signal only when selected members of saidsequence simultaneously generate pulses.

6. A pulse group discriminator comprising, pulse width discriminatormeans producing triggering pulses from applied electrical impulses, asequence of multivibrator means each for generating a time intervaldefining pulse in. response to a triggering pulse, a plurality ofshielding tubes each connecting a precedent member and a subsequentmember of said sequence, each of said shielding tubes being soresponsive to the pulse generated by its associated precedent memberthat, only during the time interval defined thereby does said shieldingtube permit the application of triggering pulses to its associatedsubsequent member, said pulse width discriminator means being connectedto the first member of said sequence and, through each of said pluralityof shielding tubes, to each of the succeeding members of said sequence,and means producing an output signal only in response to a pulsegenerated by the last member of said sequence.

7. A pulse group discriminator comprising, a pulse width discriminatormeans producing triggering pulses from only those of applied electricalimpulses which exceed in duration a predetermined duration, a sequenceof multivibrator means each for generating a time interval definingpulse in response to a triggering pulse, the interval definedby thepulse generated by each successive member of said sequence beingprogressively shorter, a plurality of shielding tubes each connecting aprecedent member and a subsequent member of said sequence, each of saidshielding tubes being so responsive to the pulse generated by itsassociated precedent member that, only during the time interval definedthereby does said shielding tube permit the application of triggeringpulses to its associated subsequent member, a phase inverting means,said pulse width discriminator means being connected to the first memberof said sequence and, through said phase inverting means and each ofsaid plurality of shielding tubes, to each of the succeeding members ofsaid sequence, and amplitude responsive means producing an output signalonly when selected members of said sequence simultaneously generatepulses.

8. A pulse group discriminator comprising, a pulse width discriminatormeans producing triggering pulses from only those of applied electricalimpulses which exceed in duration a predetermined duration, a sequenceof four multivibrator means each for generating a time interval definingpulse in response to a triggering pulse, the

pulse generated by the first member of said sequence in response to atriggering pulse having a duration at least equal to the minimuminterval required for the production of three subsequent triggeringpulses, the pulse generated by the second member of said sequence inresponse to a triggering pulse having a duration at least equal to theminimum interval required for the production of two subsequenttriggering pulses, the pulse generated by the third member of saidsequence in response to a triggering pulse having a duration at leastequal to the minimum interval required for the production of onesubsequent triggering pulse, a plurality of shielding tubes eachconnecting a precedent member and a subsequent member of said sequence,each of said shielding tubes being so responsive to the pulse generatedby its associated precedent member that, only during the time intervaldefined thereby does said shielding tube permit the application oftriggering pulses to its associated subsequent member, a phase invertingmeans, said pulse width discriminator means being connected to the firstmember of said sequence and, through said phase inverting means and eachof said plurality of shielding tubes, to each of the succeeding membersof said sequence, and amplitude responsive means producing an outputsignal only when selected members of said sequence simultaneouslygenerate pulses.

9. A pulse group discriminator comprising, a pulse width discriminatormeans producing triggering pulses from only those of applied electricalimpulses which exceed in duration a predetermined duration, a sequenceof multivibrator means each for generating a time interval definingpulse in response to a triggering pulse, the interval defined by thepulse generated by each successive member of said sequence except thelast in response to a triggering pulse having a duration at least equalto the interval required for the production of one subsequent triggeringpulse, a plurality of shielding tubes each connecting a precedent memberand a subsequent member of said sequence, each of said shielding tubesbeing so responsive to the pulse generated by its associated precedentmember that, only during the time interval defined thereby does saidshielding tube permit the application of triggering pulses to itsassociated subsequent member, a phase inverting means, said pulse Widthdiscriminator means being connected to the first member of said sequenceand, through said phase inverting means and each of said plurality ofshielding tubes, to each of the succeeding members of said sequence, andmeans producing an output pulse only in response to a pulse generated bythe last member of said sequence.

10. A pulse group discriminator comprising, at least one pulse widthdiscriminating means producing triggering pulses from each of only thoseof applied electrical impulses which possess certain predeterminedduration characteristics, a plurality of serially arranged multivibratormeans for generating a time interval defining pulse in response to saidtriggering pulses, a plurality of shielding tubes so interconnectingsaid series of multivibrator means and said pulse width discriminatingmeans as to prevent the application of triggering pulses to each, exceptthe first, of said series of multivibrator means except during the timeinterval defined by the pulse generated by the immediately preceding oneof said multivibrator means, and means producing an output pulse onlywhen said triggering pulses are so time related as to cause said seriesof multivibrator means to respond successively.

CONRAD H. HOEPPNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,655,689 Chauveau Jan. 10, 19281,763,390 Davis June 10, 1930 2,158,285 Koch May 16, 1939 2,255,162 HartSept. 9, 1941 2,325,829 Boswau Aug. 3, 1943 2,400,574 Rea et a1 May 21,1946 2,403,561 Smith July 9, 1946

